Update Intl.DurationFormat tests

[anba]

Update Intl.DurationFormat tests to match the current draft spec and add tests to cover:

• Fix and simplify "displayRequired" computation in PartitionDurationFormatPattern proposal-intl-duration-format#183
• Editorial: Add negative sign when value is 0 proposal-intl-duration-format#184

[ptomato]

For future reference, I'm not at all a fan of the approach of essentially putting a polyfill into the testIntl helper file and comparing the results from the polyfill with the results from the implementation. It makes these tests opaque, difficult to understand what's being tested, and unclear whether the polyfill or the implementation is at fault when the tests fail.

However, the tests were already set up that way, so in the absence of clear recommendations about what to do otherwise (#3786) I would say that changing it is out of scope for this PR.

Nonetheless I would suggest that numeric-hour-with-zero-minutes-and-non-zero-seconds.js was clearer using NumberFormat and ListFormat directly, as it previously did, so maybe we should drop the commit ' Use formatDurationFormatPattern for "/numeric-hour-with-zero-minutes-and-non-zero-seconds"'.

Could @ryzokuken, @romulocintra, or @ben-allen take a look at the polyfill changes please?

[anba]

Nonetheless I would suggest that numeric-hour-with-zero-minutes-and-non-zero-seconds.js was clearer using NumberFormat and ListFormat directly, as it previously did, so maybe we should drop the commit ' Use formatDurationFormatPattern for "/numeric-hour-with-zero-minutes-and-non-zero-seconds"'.

This isn't actually possible, because of tc39/proposal-intl-duration-format#180. Before that PR, the test expected the string "1, 03", so the hours and seconds duration units were number-formatted and then concatenated through the list formatter. After the PR, the expected string is "1:00:03", so the list formatter is no longer used at all. The only alternative here is to hardcode the string "1:00:03" as the expected result and don't use a number nor a list formatter.

[ben-allen]

With regard to the "numeric-hour-with-zero-minutes-and-non-zero-seconds" question: in recent tests involving digital-like styles (see: #4034) I've been handling them by stitching together the unit values with ":" as a hard-coded separator. My theory is that this is slightly better than using a fully hard-coded string, since:

1. Tests written this way could in the future be used to test in other locales that also use ":" as the hours/minutes and minutes/seconds separators, but that use different numbering systems
2. It makes it relatively simpler to (in the somewhat more distant future) draw from the new [[HoursMinutesSeparator]], and [[MinutesSecondsSeparator]] slots from Editorial: Refactor handling of numeric-like styles, support differing hours/minutes vs minutes/seconds separators proposal-intl-duration-format#188

[ben-allen]

oh my goodness, thank you for catching this. I'm actively embarassed...

[ben-allen]

It's all great -- thank you for all of your work here.

Thoughts in general:

• I'm wondering if it's worthwhile to have a TG2 discussion on the behaviour when seconds (or the relevant subsecond unit) has its display option set to "auto" and has a non-zero fractional component that's nevertheless not displayed due to use of the fractionalDigits option. I can see arguments for changing this behaviour, but also arguments for leaving it as-is
• I share @ptomato's skepticism about the use of the partitionDurationFormatPattern quasi-polyfill. That said, given that these tests are great and given that DurationFormat is nearly done, I'm wondering if, in the interest of testing locales other than "en", it would be useful for me to extend partitionDurationFormatPattern to handle hour/minute/second separators other than ":", decimal separators other than ".", and numbering systems other than latn.